Is a 4 10 bullet a 20 Gage bullet?

Answer 1

I think what you're asking is:

Is a .410 bullet a 20 gauge bullet??

Well, most shotguns are sized using the Gauge nomenclature. Generally, gauge answers:

"How many lead spheres of this diameter are needed to equal a pound?"

So, the larger the diameter, the larger the spheres of lead, the fewer are needed to equal a pound. So that is why the gauge system is inverted (lower number equals a larger bore: a 12 gauge has a larger diameter than a 20 gauge.

There is a shotgun size that does NOT use gauge, it uses caliber (like a bullet). This exception is the .410 shotgun--The .410 is 41/100ths of an inch, or roughly .41 caliber.

Also, shotguns usually propel several projectiles at once (called shot). This can range from the size of sand grains to marble sized pellets. Some shotgun cartridges fire a single chunk of lead which is called a SLUG (not a bullet).

So to answer your (cleaned-up) question, a .410 slug is much much smaller than a 20 gauge slug. A rough estimate is that a .410 barrel is roughly 68 gauge, while a 20 gauge is roughly .60 caliber.